Automatic particle analysing system

ABSTRACT

A method and an apparatus for automatical analysis of particle size distribution, shape and colour, comprising collection of a particle sample, where the aprticles are distributed into a substantially monolayer particle curtain to be exposed to a light source for providing imaging and subsequent analysis of the particles. The apparatus has a sampling device that collects samples from the product stream integrated in the system.

[0001] The present invention relates to a method and an apparatus forautomatic sampling and for performing an automatic image analysis todetermine a particle size distribution, shape characterization and shapedistribution.

[0002] It is important for example in the fertilizer industry to havereliable information about the end product size distribution andparticle shape, as optimal values for these parameters are of importanceboth from a purely economical point of view and when using the product,e.g. when spreading the produced prills or granules. Furthermore, aprocess will be most economical if it gives a product with a narrowsieve span, without having to sieve away large fractions that have to berun in return.

[0003] A method and apparatus for this use is earlier known from U.S.Pat. No. 5,011,285. The method includes the collection of particlesamples and the generation of a particle curtain in a monolayer form.The particle curtain is formed by taking particles through a silo downonto a vibrating plate. The particle curtain is lit up and the images ofthe particles therein is recorded and analysed. The silo has at leastone level sensor to record the level of particles in the silo and togive a signal to the sampler.

[0004] In U.S. Pat. No. 5,309,215 there is also shown an apparatus forthe determination of particle size distribution based on the sameprinciple. Particles are fed from a sample collection chamber to aconveyor band or vibrating channel forming a particle curtain whenfalling down from this band or channel.

[0005] Both these methods are dependent on a separate collection of thesamples. The samplers commonly used in such processes are conveyor beltsamplers comprising for example a container with a longitudinal slitthat passes across the product stream on the conveyor belt or collectsthe samples at the end of the conveyor belt in such a way that theparticles can fall gravimetrically into the sampler when it transversethe product stream. Also in production pipes, samplers collectsparticles from a cross section of the product stream.

[0006] The samples thereafter have to be transferred to thecontainer/sample collection chamber before they can be analysed. Toinstall such a sampling and analysing system often involvescomprehensive reconstruction of the production line to fit a samplingsystem, if at all possible. For example by installation of an end ofconveyor belt sampler, the end of conveyor belt housing (covering) hasto be reconstructed to fit the sampling system. The expense of such acomprehensive reconstruction of the process line can be a reason not toinvest in an imaging analysis equipment. For some installations it couldalso be very difficult to find space in the process line for a samplingsystem or to find a sampling system that could be used in an existingprocess.

[0007] The object of the invention is to obtain a simple, sturdy andcheap particle analyser that easily can be used in existing productionfacilities without extra investments and reconstruction. Another objectis to arrive at a versatile and automatic method and apparatus foranalysis of a plurality of samples applicable for on-line analysis.

[0008] These and other objects of the invention are obtained with themethod and apparatus as described below, and the invention is furtherdefined and characterised by the accompanying patent claims.

[0009] The invention thus concerns an automatic particle analysingsystem and a method for automatical analysis of particle sizedistribution, shape and colour. The analysing system comprises samplingmeans and a device for creating a particle mono curtain suitable forimaging and subsequent analysis, wherein a sampling device is anintegrated part of the system. The sampling device could be a tubemoveable from a lower sampling position to an upright position where thesample is transferred directly on to a vibrating plate/trough forcreating a particle curtain. Alternatively, the sampling device is aplate/trough that is vertically movable from a lower sampling positionto an upper position where it is used to create a particle curtain. Theplate/trough could be rectangular with an end wall and parallell sidewalls or be a plate with non parallel side walls. The sampling device,device for distributing the sample into a mono curtain, light source andrecording means are all mounted to a frame that could be fixed to aconveyor belt.

[0010] The integrated sampling device collects samples directly from theproduct stream. It is preferred to collect a vertical cross section ofthe product stream and do the sampling countercurrent to the productstream. It is preferred to use a sampling tube which is verticallymovable from a lower sampling position to an upright position where thesample is fed directly to a vibrating plate for creating a particlecurtain. Alternatively, the sample is collected by lowering thevibrating plate/trough into the product stream and thereafter liftingthe plate to an upper position where the plate is vibrated to create aparticle curtain. A new sample is automatically collected when the lastparticle on the plate is analysed.

[0011] The invention will now be further explained in the followingembodiments with reference to the accompanying drawings, FIGS. 1-4,wherein

[0012]FIG. 1A shows a perspective view of a particle analyser with thesampler tube in a lower sampling position.

[0013]FIG. 1B shows a view with the sampler in a lower samplingposition.

[0014]FIG. 2 shows a perspective view with the sampler tube in upperposition (emptying sample to the vibrating system).

[0015]FIG. 3A shows a perspective view of an alternative configurationof the particle analyser with sampler in upper position.

[0016]FIG. 3B shows a side view with the analyser with vibrating platesampler in upper position.

[0017]FIG. 4A shows a perspective view of the alternative configurationof the particle analyser with sampler in sampling position

[0018]FIG. 4B shows the analyser with vibrating plate sampler in lowerposition.

[0019] A particle analyser 1 is shown in FIGS. 1A, B and 2, including asampler 2 to collect particle samples in a process, for example at aconveyor belt 3 as shown in the figures. The conveyor belt is mountedupon a frame 4. The sampler 2 is shown as a tube with a bended lowerpart. The sampler is movable vertically fixed to a mounting frame 5. Theframe has two vertically extending legs adapted to be fixed to theconveyor belt frame 4, and an upper horisontal part, to which the othercomponents of the analyser are fixed. A pneumatic cylinder 6 is used todrive the sampler between an upper and lower position. In FIGS. 1A and Bthe sampling tube is shown in its lower sampling position collectingsamples into one end of the tube in the product stream on the conveyorbelt, while FIG. 2 illustrates the sampler in upright position where thecollected sample is falling from the sample collected end of the tube onto a plate 7 or trough. The plate 7 is mounted to a vibrator 8 which mayvibrate in a known manner, and both the frequency and the amplitude maybe regulated. In these figures the vibrator 8 is shown mounted below theplate 7. By vibrating the plate the particles will run out over its edgecreating a particle curtain. By adjusting the vibration amplitude and/orfrequency, one can easily make sure that the particles fall down fromthe plate into a substantially monolayer of particles. This iscontrolled by a computer and thus overlapping particles in the image isavoided.

[0020] The sampler could be of different design. It could be in the formof a straight or bended pipe. A pipe with a rectangular cross section isalso possible to use. What is most important is that it has a shape thatmakes it possible to collect samples in the product stream. It is alsoimportant that the diameter of a pipe sampler is at least 2-3 times thediameter of the product to be analysed, to make sure that there is afree flow of the product.

[0021] A light source 9 is mounted to the frame 5 below the vibratingplate 7. The particle stream or particle curtain is thus lit up by thislight source. The light source could be a normal lamp, a set of laserbeams or a flash which lights at a signal. A unit 10 mounted at theother side of the frame may be a film or video camera, but also arecording unit for penetrating light, for example laser beams. Theparticle stream from the vibrating plate thus falls between the lightsource and camera 10. A video camera taking images all the time ispreferably used, but if the light source is a flash the images will berecorded only at each flash. By using a video camera to take pictures ofthe monolayer of particles pictures are obtained. Thereby both theirshape and size distribution could be registered. Special computerprograms for the calculation of shape characterisation or the deviationfrom the desired shape are used and the particle size distribution inthe product stream determined. Generation of the particle curtain andanalysing the particles an be carried out continuously, and theproduction parameters can be adjusted as a unction of the result of theanalysis.

[0022] The vibrating plate or trough, is shown in FIGS. 1A, B and 2 as arectangular plate with one end wall and two parallel side walls. Thisshape is especially used for coarse particles. For smaller particlesproduct, a vibrating plate with not parallel side walls can be used,giving a narrower passage for the particles before they fall over theedge forming a particle curtain. When imaging small particles products,the camera 10 must be put closer to the product and it is therefore notnecessary with a very wide particle curtain. The computer will regulatethe number of particles. The passage out from the trough should at leastbe 2-3 times the largest diameter of the particles. However, if wanted,it is possible to mount more than one camera to cover a wider particlearea or different camera selection for different particle ranges. Whichshape of the trough that is selected, will be dependent on the productto be analysed.

[0023] Instead of using a sampling device as illustrated in FIGS. 1 and2, it is also possible to use the vibrating trough to collect thesamples. An alternative particle analyser is illustrated in FIGS. 3 and4. The vibrating trough 7 is shown mounted below the vibrator 8 to aframe 5 (FIG. 4). This frame has an upper horisontal part and fourvertical legs to be monted on opposite sides of the conveyor frame 4.Pneumatic cylinders 6 fixed to the frame 5, lower the trough 7 down intothe product stream on the conveyor belt 3 as illustrated in FIG. 4. Asample is collected and the trough is lifted to the upper position asillustrated in FIG. 3. Thereafter the vibrator is activated and aparticle curtain is formed, imaged by using flash 9 and camera 10,recorded and analysed. When the trough is empty, a new sample iscollected.

[0024] When using the apparatus according to the invention, sampling iscarried out counter-current to the product stream on the conveyor belt.The sampler is lowered into the product stream. A vertical cross sectionof the product is collected and this will be close to an averageparticle distribution. This will result in samples that arerepresentative enough to control a production process.

[0025] Each time all the particles in the sample are analysed, thesampler will move to the product stream again to collect a new sample.The analysed sample falls directly down on to the conveyor belt again.In this way analysis and sampling is repeated continuously. However, itis also possible to control the sampling frequency in other ways. Oftenit could be sufficient just to analyse a certain number of particles ina sample. The vibrating plate will be emptied of particles before a newsample is taken. It is also possible to take product samples at setintervals.

[0026] The mounting frame 5 should be fixed to the frame 4 of aconveyor. It could be mounted on the one side of the conveyor belt asillustrated in FIGS. 1 and 2 or across the conveyor belt as illustratedin FIGS. 3 and 4. It is preferred to mount the frame in the longitudinaldirection. This makes it easier to adjust the camera when this isnecessary.

[0027] The method and the apparatus according to the invention may beapplied to all known particlulating processes and processes whereaddition of particles with the desire size distribution and shape isimportant. The invention could be used to analyse all kind of dryparticles, apart from fertiliser, for example broken stone, sand,products in the food industry etc. The invention will, however, beapplicable for verification of finished particulate product too. Suchapplication may be: analysis during bulk loading, packing in bags or thelike or verification of the specification of particulate products. Theinvention could be used both for conveyor belt or pipelineinstallations.

1-13. (Cancelled)
 14. Automatic particle analyzing system comprising asampling device and a device for creating a particle curtain in amonolayer form suitable for imaging and subsequent analysis, wherein asampling device (2) is an integrated part of the system.
 15. Analyzingsystem according to claim 14, wherein the sampling device (2) is a tubemoveable from a lower sampling position to an upright position where thesample is transferred directly on to a vibrating plate/trough (7) forcreating a particle curtain.
 16. Analyzing system according to claim 14,wherein the sampling device is a plate/trough (7) that is verticallymovable from a lower sampling position to an upper position where it isused for creating a particle curtain.
 17. Analyzing system according toclaim 15, wherein the plate/trough (7) is rectangular with an end walland parallel side walls.
 18. Analyzing system according to claim 15,wherein the plate/trough (7) has non parallel side walls.
 19. Analyzingsystem according to claim 14, wherein the device for sampling (2),device for distributing the sample into a mono curtain (7,8), lightsource (9) and recording means (10) are mounted to a frame (5) adaptedto be fixed to a conveyor frame (4).
 20. Analyzing system according toclaim 19, wherein the frame (5) is adapted to be mounted across theconveyor belt or along one side.
 21. A method for automatical analysisof particle size distribution, shape and colour, comprising collectionof a particle sample and distributing the particles into substantially aparticle curtain in a monolayer form, that is to be exposed to a lightsource for providing imaging and subsequent analysis of the particles,wherein a sampling device that collects samples from the product streamis integrated in the system.
 22. Method according to claim 21, wherein avertical cross section of the product stream is collected.
 23. Methodaccording to claim 21, wherein sampling is carried out countercurrent tothe product stream.
 24. Method according to claim 21, wherein a samplingtube is used, which is movable from a lower sampling position to anupright position where the sample is fed directly to a vibrating platefor creating a particle curtain.
 25. Method according to claim 21,wherein a the sample is collected by lowering a plate/trough into theproduct stream and thereafter lifting the plate to an upper positionwhere the plate is vibrated to create a particle curtain.
 26. Methodaccording to claim 24, wherein a new sample is automatically collectedwhen the last particle on the plate is analyzed.
 27. Analyzing systemaccording to claim 16, wherein the plate/trough (7) is rectangular withan end wall and parallel side walls.
 28. Analyzing system according toclaim 16, wherein the plate/trough (7) has non parallel side walls. 29.Method according to claim 25, wherein a new sample is automaticallycollected when the last particle on the plate is analyzed.